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Three new tetranuclear iron(III) and zinc(II) complexes, [Fe(cpdp)(phth)(OH)]·8HO (1), [Fe(cpdp)(terephth)(OH)] (2), and [Zn(Hcpdp)(suc)]Br·12HO (3), have been synthesized as models for the active site of phosphoester hydrolases by utilizing a polydentate ligand, N, N'-bis[2-carboxybenzomethyl]- N, N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol (Hcpdp) in combination with exogeneous phthalate (phth), terephthalate (terephth), and succinate (suc). Single crystal X-ray analyses reveal that the metallic core of complex 1 consists of four distorted octahedral iron(III) ions with average intraligand Fe---Fe separation of 3.656(2) Å, while the structure 3 represents a tetranuclear metallic core containing four distorted trigonal bipyramidal zinc(II) ions with average intraligand Zn---Zn separation of 3.472(2) Å. The molecular structure of complex 2 has been optimized by the DFT method which shows that its core arrangement is similar to that of 1. Complex 1 has a very interesting centrosymmetric structure that includes two crystallographically equivalent [Fe(cpdp)] dinuclear units, connected together by a pair of syn-syn bridging phthalates and a pair of bridging hydroxides to generate a "dimer of dimers" structural motif. In complex 3, a succinate group connects two crystallographically equivalent [Zn(Hcpdp)] dinuclear units in a syn-syn bidentate manner forming a "dimer of dimers" structural design. All three complexes show phosphatase-like activity that has been examined in methanol-water (1:1; v/v) using bis( p-nitrophenyl) phosphate (BNPP) as model substrate by applying the UV-vis spectrophotometric technique. In each case, the kinetic data have been analyzed by the Michaelis-Menten approach. The order of catalytic efficiency for the conversion of substrate to product follows the trend 1 > 2 > 3 with turnover rates ( k) of (2.73 ± 0.13) × 10 for 1, (1.06 ± 0.07) × 10 for 2, and (2.33 ± 0.18) × 10 s for 3. These k values are comparable to, albeit slightly lower than, the values reported for similar iron(III)- and zinc(II)-based model complexes in the literature. DFT calculations have been carried out to support the proposed mechanism for phosphatase-like activity.

Three, PO 4 3– /HPO 4 2– and AsO 4 3– -incorporated, new tetranuclear complexes of copper(II) and zinc(II) ions have been synthesized and fully characterized. In methanol–water, reactions of H 3 cpdp (H 3 cpdp = N , N ′-Bis[2-carboxybenzomethyl]- N , N ′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II) chloride in the presence of either NaOH/Na 2 HPO 4 ·2H 2 O or KOH/Na 2 HAsO 4 ·7H 2 O lead to the isolation of the tetranuclear complexes Na 3 [Cu 4 (cpdp) 2 (μ 4 -PO 4 )](OH) 2 ·14H 2 O ( 1 ) and K 2 [Cu 4 (cpdp) 2 (μ 4 -AsO 4 )](OH)·16 2 / 3 H 2 O ( 2 ), respectively. Similarly, the reaction of H 3 cpdp with zinc(II) chloride in the presence of NaOH/Na 2 HPO 4 ·2H 2 O yields a tetranuclear complex, Na(H 3 O) 2 [Zn 4 (cpdp) 2 (μ 4 -HPO 4 )]Cl 3 ·12 1 / 2 H 2 O ( 3 ). All complexes are characterized by single-crystal X-ray diffraction and other analytical techniques, such as Fourier transform infrared and UV−vis spectroscopy, thermogravimetric and electrochemical studies. The solid-state molecular framework of each complex contains two monocationic [M 2 (cpdp)] + (M = Cu, Zn) units, which are exclusively coordinated to either phosphate/hydrogen phosphate or arsenate groups in a unique mode. All three complexes exhibit a μ 4 :η 1 :η 1 :η 1 :η 1 bridging mode of the PO 4 3– /HPO 4 2– /AsO 4 3– groups, with each bridging among four metal ions. The thermal properties of all three complexes have been investigated by thermogravimetric analysis. Low-temperature magnetic studies of complexes 1 and 2 disclose moderate antiferromagnetic interactions mediated among the copper centers through alkoxi...

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